They are probably saying RMT is related to mystic because RMT can expedite the process of obtaining mystic.
Currently, the best way to obtain mystic other than reputation spark is farming Belial. If you can RMT and buy a ton of Belial mats from dupers, then it becomes much easier to find mystics. You just have to spend the time to farm Belial.
Belial farming also happens to give you a lot of ash. So now you can farm Ash and convert it to scroll and have an alt complete the reputation board for free spark.
So while RMT will not directly get you mystic items, it will make it easier by many factors.